The endemic Telestes species are among the most endangered freshwater fish in Europe, in Croatia lives eight of them. Due to the burden of freshwater ecosystems, habitat degradation, melioration, water regulation and invasive species, Telestes is classified into the critically endangered IUCN Red List category. To propose adequate protection measures and expand knowledge of biology, ecology and genetics of these species, I calculated the variations of DNA sequences among populations, estimated the population correlation and their effective size, and carried the species through different scenarios of potential disasters to test their viability. Populations migrates are not reciprocal, more and more migrants migrate in one direction - downstream, upstream and underground. Since the effective sizes of all the investigated species are relatively small, they are more sensitive to changes in the environment. The most vulnerable species is T. karsticus, and the most resistant are T. turskyi and T. fontinalis.